Method of strengthening and sealing rock



Dec. 14, 1965 Filed May 2. 1961 U. M. LANGEFORS ET AL METHOD OFSTRENGTHENING AND SEALING BOOK 2 Sheets-Sheet 1 Dec. 14, 1965 u. M.LANGEFORS ETAL 3,

METHOD OF STRENGTHENING AND SEALING ROCK Filed May 2, 1961 2Sheets-Sheet 2 United States Patent l 3,222,872 METHGD 0F STRENGTHENHNGAND SEAHNG RUCK Ulf Marten Langefors, Stoekhoim, and Sten HaraldBrannfors, Lidingo, Sweden, assignors to Nitrogiycerin Aktiebolaget,Gyttorp, Sweden Filed May 2, 1961, Ser. No. 107,175 Claims priority,application Sweden, May 5, 1960, 4,474/60 9 Claims. ((11. 61-36) Thepresent invention relates to the strengthening and/ or tightening, orsealing of rock by so-called injection or spreading of a binding orsealing medium either in cracks or faults inside the rock or over partsof a rock surface uncovered by blasting.

In all rock-working by blasting it is important to ensure that only theintended parts of the rock are detached by the blasts. For variousreasons, such as natural crack formations and other local weaknesses inthe rock, there is often a risk, however, of unintended subsequent slipsof material and furthermore in tunnel work, for example, the blastingoperations may create open communications to veins of water present inthe rock so that the progress of the work is hindered by a heavy outflowof water.

In order to avoid such disturbances it is well known to strengthenand/or tighten the weak parts of the rock by injecting a binding orsealing medium and to improve the tightness and strength of an uncoveredrock surface by applying a covering layer of a rapidly solidifyingsealing medium to the same by spraying for example.

The injection of a binding or sealing medium is usually effected bypumping in some hydraulic cement composition, such as Portland cementslurry or concrete through drill holes, especially prepared for thatpurpose. Preparatory to such injection it has also been suggested toestablish an improved communication between the drill hole and theadjoining natural cracks and faults in the rock by firing a limitedblasting charge in the hole to thereby provide for a locally increasedartificial crack formation and hence facilitate the distribution of theinjection medium. After its injection the injection medium is, ofcourse, allowed to bind before further work is done on the rock.

In many cases, however, it is not possible to strengthen the rock to adesired extent by injections made in advance of blasting, or suchinjections may for some other reason he insufiicient to avoidcomplications and disturbances during the subsequent rock blasting work.Under such circumstances some sort of surface-strengthening or sealingmeasures must be resorted to, and it is of great importance that suchmeasures are then effected as rapidly as ever possible after theblasting so that the rock cannot start moving or the water cannot gushout in such quantities that the cracks are washed clean and will bedifficult to seal.

Obviously this is a demand which is very difficult, and sometimes risky,to fulfill when the sealing or strengthening of the surface is to beeffected by spraying the recently uncovered rock surface with concretefor example.

The present invention has for its main object to con siderably improvethe possibilities for effectively spreading injection or sealingmaterials in order to strengthen and/or seal the rock. According to theinvention this improvement is achieved by utilizing the gas pressurefrom a detonating blasting charge for spreading the binding or sealingmedium. Secondarily the temperature rise occurring at the detonation ofthe explosive can be used to facilitate the distribution of the bindingor sealing medium.

According to the invention, not only can the injection or spreading ofthe binding or sealing medium be carried 3,222,872 Patented Dec. 14,1965 out without the help of any special equipments in the form of pumpsor the like but, at the same time, improved spreading is achieved bothas a result of the high pressure available and also owing to the factthat the cracks in the vicinity of a detonating change at the actualmoment of blasting are expanded by the gas pressure so that thepenetration of the medium will be facilitated.

The invention can be applied both for the injection of a binding orsealing medium in advance and for spreading the medium in directconnection with such blasts which have for their purpose to uncoverfresh rock surfaces. In the later case the invention supplements orreplaces in a very favorable manner the subsequent application of acovering layer mentioned in the introduction, since according to theinvention the binding or sealing medium is driven into the cracks in theremaining rock surface with considerable force and thus effectivelybinds the latter to a considerable depth. Therefore, also in this case,the treatment may be referred to as a kind of injection although a partof the binding or sealing agent will then, of course, 'be lost becausesome of the agent will become distributed over the surfaces of suchblocks or pieces of the rock which are removed by the blast.

The application of the invention in direct connection with the removalof rock by blasting may in certain cases advantageously replace thestrengthening of the rock by injection before the blasting work isstarted. When undertaking such preparatory injection there is, namely, aconsiderable risk that the bond formed between the parts of the rockwill be again broken apart at the momentary expansion of the cracksduring the subsequent blasting. In contradistinction thereto, byinjecting a binding or sealing medium in connection with the blastingaway of the rock according to the present invention the adhesion of themedium first begins when the cracks are subjected to the pressure of thegases of explosion and are thus expanded, and the subsequent hardeningor solidification of the medium generally occurs first when the blastingprocess has already taken place and the cracks have contracted again.This, however, requires that the hardening or solidifying process takeplace rapidly.

Obviously the basic inventive idea may be applied in many differentways. For example, the binding or sealing medium and the blastingcharge, respectively, may each be introduced as separate units into adrill hole, whereupon the blasting charge is caused to detonate, or thebinding or sealing medium and the blasting charge may be introducedtogether into a drill hole as a single unit prepared in advance.

The magnitude of the blasting charge must, of course, be adapted to thedesired effect, which in case of a preparatory injection may consistsolely of the spreading or blowing in of the medium into existing holesand cracks, but it may also include the blasting of communicating cracksbetween a drill hole and the natural crack formations in the rock, sothat the need for a separate blast in the hole before the injectionproper is entirely eliminated. In addition, as already mentioned, theblasting charge can be utilized for positively detaching material from arock surface while, at the: same time, it causes a spreading of thebinding or sealing medium not only over considerable parts of the rocksurface exposed by blasting but also into cracks and faults in suchsurface.

The invention may, of course, very well be applied in its primary formtogether with a fluid injection medium e.g. in the form of a cementslurry or concrete, which should then preferably be of the rapidhardening type. In view of the new technical aspects offered by theinvention, however, it is also possible to employ other types of bindingor sealing media than just suspensions of this kind. Thus, it ispossible by means of a blasting charge to spread a hydraulic bindingmedium such as cement also in a pulverulent form. In such a case themedium may, if desired, be compressed beforehand into a solid body orbriquette which is pulverized during the explosion in the blasting. Ahydraulic binding medium of this kind can then be caused to bind andharden rapidly in the cracks and holes of the rock by the addition ofwater produced by the detonation of the explosive, or deriving from thenatural supply of water which can be counted on from the water veins inthe rock itself. If this supply of water should be insufiicient, thecharge itself may be supplemented either by the addition of a watercapsule which is split up by the explosion, or by submerging the chargein water before it is inserted into the hole, the water then suitablybeing absorbed in an ample quantity in a porous paper wrapping, forexample, surrounding the binding medium unit itself. The water may, ofcourse, be replaced by some other additional liquid agent which causesbinding and hardening. By way of a further example it may be mentionedthat the hydraulic binding medium may be substituted by a partiallypolymerized synthetic resin composition and the water by a hardener oraccelerator to rapidly cause complete polymerization of the same.

In place of media of the type just mentioned, there may also be usedsealing media in the form of particular, hydrophilized asphaltcompositions, thermo-plastics or similar materials, the viscosity ofwhich may be reduced by the heat produced during the explosion, so thatthe material can easily flow into thin cracks, etc. under the pressureexerted by the gases of explosion. These latter media may, of course,also be shaped into briquettes or solid bodies which are disintegratedby the detonation.

To further elucidate the invention some applications of the process aswell as some forms of charges to be used have been illustrated in theaccompanying drawings, in which FIG. 1 is a sectional elevation takenthrough part of a rock in which a tunnel is in course of construction byblasting; I

FIG. 2 shows to an enlarged scale a vertical section through a fragmentof a tunnel back or root;

FIG. 3 is a longitudinal section through a drill hole containing acharge which consists of an explosive and a binding or sealing medium,and

FIG. 4 shows a cross-section through another drill hole having insertedthereinto a charge comprising both a dry binding medium, a liquidcapsule and a central blasting charge.

FIG. 1 shows, on the top lefthand side, a typical example of aninjection drill hole 1, through which a binding or sealing medium forlocal tightening or strengthening of the rock can be injected into arock portion containing numerous cracks as indicated, in the Vicinity ofthe lower end of the drill hole. In a downwardly directed injection holeof this kind one may advantageously use the most simple form ofapplication of the inventive process which consists in first pouring acertain quantity of fluid concrete or cement slurry into the hole andthen submerging into the fluid contents of the hole a blasting charge,which is subsequently fired, so as to both blast apart the walls of thedrill hole to establish communication between the hole and the adjacentnatural cracks in the rock, and also spread the concrete or cementslurry into the cavities and cracks in the weak part of the rock withconsiderable force.

It will be apparent that a fluid medium, such as the cement slurry orconcrete mass mentioned, is not so handy to use where the drill holesextend horizontally or upwardly from below as may frequently be thecase. In such cases, injection may more suitably be carried out withsealing media in solid or at least plastic form so that the medium maybe introduced into the drill hole in pieces of suitable shape tosurround the blasting charge proper. Such ,a procedure as well ascharging the drill hole with a prefabricated composite charge containingboth an explosive and a suitable quantity of sealing mass, as will bereferred to hereinafter, may, of course, always be used for injectionirrespective of the location of the drill hole.

The tunnel 2 indicated in FIG. 1 is in course of being extended in anupward direction and a series of substantially horizontal drill holes 3have therefore been provided in that part of the rock which forms theback or roof of the tunnel. According to the invention, charging unitspreferably prepared in advance and of a type which will be moreparticularly described hereinafter with reference to FIGS. 3 and 4 areinserted into these drill holes 3. The purpose of these charges is notonly to detach material from the tunnel back, but at the same time theyshould produce a strengthening of the new roof surface in the tunneluncovered by the blast, by spreading a binding or sealing medium bothover considerable parts of the fresh rock surface to be exposed and alsointo such cracks and cavities in said fresh surface which already existor are produced as a result of the blast.

FIG. 2 shows in an enlarged scale a fragment of a tunnel roof surfacenewly uncovered by blasting. In this figure the thickened radiatinglines and contours 4 indicate the surfaces and cracks over which thebinding or sealing medium is spread by the charge 5, indicated bydash-and-dot lines. It should be immediately obvious that by a suitabledistribution of the drill holes and the charges a practically continuousspreading of the binding or sealing medium over the entire uncoveredsurface may be obtained, this being, however, not always necessary oreven desirable. When calculating the intermediate distances between thedrill holes it should also be borne in mind that the spreading of thebinding or sealing medium over the exposed rock surface is alwaysappreciably greater than the penetration of the medium into the racks,etc. It should also be noted that the explosive charge even in thelast-mentioned type of blasting may to a considerable extent assist inproducing new communications between the drill holes and the naturalcracks in the rock so that spreading of the binding or sealing medium isfacilitated.

In FIG. 3 there is shown in shortened longitudinal section a drill hole6 with a sealing charge intended for simultaneous blasting away of therock. This composite charge which is inserted into the hole in the usualmanner inside a stemming 7, is in the form of a rod which may, ifdesired, be assembled from a number of sections, and which consists ofan outer tubular casing 8 formed by a binding or sealing medium and aninner core of an explosive substance 9. The two parts 8 and 9 of thecharge may, of course, be stored and transported to the working siteseparately to be assembled to a unit first when inserted into the drillhole, but the parts of the charge may also be combined in a single unitalready at the factory producing the explosive.

In FIG. 3 the tubular casing 8 may be moulded from a quick-settinghydraulic cement in a dry, powdered state, for example, but compressedto form a kind of briquet (of course without any addition of water).Alternatively the casing 8 may be moulded of a thermo-plastic resin or asimilar composition, such as hydrophilized asphalt.

On the other hand, it should be understood that the binding or sealingmedium may also be introduced into the drill hole at the working sitewithout being preshaped to tubular bodies. Thus the sealing medium, ifin the form of a dry cement powder, may be blown or stamped into thedrill hole and the filling or plug formed thereby be hollowed to receivethe explosive charge. Stamping and hollowing may, of course, also beused in connection with binding or sealing media in plastic form, and issometimes the most convenient method, the more since it is notabsolutely necessary to locate the explosive substance 9 centrally inthe filling or tube of the sealing agent. In certain cases an eccentriclocation of the explosive may even be advantageous in order to produce amore controlled distribution of the binding or sealing material incertain predetermined directions.

Far more important from the point of view dealing with best possibleutilization of the blasting charge for spreading the binding or sealingmedium in the most favorable manner over a maximum rock surface area isthe distribution of the medium in the longitudinal direction of thedrill hole. As a general rule, the seal forming material to be spreadout should be distributed as evenly as possible longitudinally of thatpart of the drill hole which is intended to receive the explosive. Thisis the reason why a substantially tubular body of sealing medium ispreferred but on the other hand, if such moulding of the medium is notdesirable, for instance because it would be rather expensive, one mayequally well use an explosive charge divided into several pieces andplace the sealing medium between such pieces spaced in the drill hole.

FIG. 4 shows a slightly modified type of composite charge in a drillhole 10, this latter charge consisting of a central core 11 of anexplosive substance surrounded by a capsule 12 containing a liquid suchas water and a tubular outer casing 13 of a binding medium, such as ahydraulic cement in dry form. The liquid capsule 12 may be constructedof a plastic material or the like for example, and it is, of course,intended to burst at the blast so that the liquid therein mixes with thedry cement derived from the outer casing 13 disintegrated by theexplosion.

The invention must, of course, in no way be considered limited to theexamples shown herein, because such examples have only been given tofacilitate understanding of the general idea. by those skilled in theart that the basic inventive principle can be applied in many differentways in order to attain the desired result, and that particularly thechoice of the binding or sealing medium to be used in the various casesis dependent upon the special requirements that are considered ofimportance at each particular working site.

What we claim is:

1. A method of creating a layer of sealing material across a broad areaof an earth formation, comprising:

(a) drilling a plurality of spaced holes in said formation;

(b) said holes being spaced a predetermined distance from one another;

(0) depositing a sealing material and an explosive material in each ofsaid holes; and

(d) detonating said explosive material;

(c) said predetermined distance between said holes being such that thepressure created by detonation of said explosive material is sufiicientto form interconnecting fractures between said holes and distribute saidsealing material throughout said fractures between said holes, whereby apractically continuous layer is formed across the earth formation bysaid sealing material.

2. A method in accordance with claim 1 wherein the sealing material isdistributed along substantially the entire length of the holes.

3. A method in accordance with claim 1 wherein the formation containswater and said water, together with dry, hydraulic cement, forms thesealing material.

4. A method in accordance with claim 1 wherein water is distributed in adry, hydraulic cement by detonation of the explosive to form the sealingmaterial.

Instead it should be readily understood 5. A method in accordance withclaim 4 wherein the water is contained in a frangible containerdeposited in the hole.

6. A method in accordance with claim 1 wherein the holes have depositedtherein elongated cartridges having the sealing material and theexplosive material distributed along their entire length.

7. A method in accordance with claim 6 wherein water in a frangiblecontainer is also located in the cartridge.

8. A method of blasting to expose a broad area of earth formation andsimultaneously seal the surface thereof, comprising:

(a) drilling a plurality of holes into the formation at a level at whichthe formation is to be removed;

(b) said holes being spaced a predetermined distance apart;

(c) depositing in each of said holes a cementitious material and anexplosive material;

(d) detonating the explosive material;

(e) said predetermined distance between said holes being such that thepressure created by the detonation of the explosive material issufficient to break away the unwanted formation and distribute apractically continuous layer of sealing material on the face of theformation between the holes, whereby the exposed surface of theformation is sealed by said sealing material.

9. A method of blasting to expose a broad area of rock formation andsimultaneously strengthen the surface thereof, comprising:

(a) drilling a plurality of holes into the formation at a level at whichthe formation is to be removed;

(b) said holes being spaced a predetermined distance apart;

(c) depositing in each of said holes a strengthening medium and anexplosive material;

((1) detonating the explosive material;

(e) said predetermined distance between said holes being such that thepressure created by the detonation of the explosive material issufiicient to break away the unwanted formation and distribute saidstrengthening medium into cracks adjoining the remaining face betweenthe holes, whereby the exposed surface of the formation is strengthenedby said sealing material.

References Cited by the Examiner UNITED STATES PATENTS 442,678 12/1890Hartley 102-23 748,935 1/1904 Durham 102-24 1,480,674 1/1924 Diescher16623 1,592,104 7/1926 Hallvarson 166-23 1,734,670 11/1929 Greene 166117X 1,934,701 11/1933 Edwards 166-23 1,987,958 1/1935 Klie 61-36 2,229,2641/ 1941 Wertz 1172 2,627,169 2/ 1953 Poulter 61-35 2,689,008 9/1954Allen et al 16623 2,718,264 9/1955 Allen 166--36 X 2,911,046 11/1959Yahn 10223 X 3,108,443 10/1963 Schuermann et a1. 61-450 CHARLES E.OCONNELL, Primary Examiner.

JACOB L. NACKENOFF, EARL I. WITMER,

Examiners.

1. A METHOD OF CREATING A LAYER OF SEALING MATERIAL ACROSS A BROAD AREA OF AN EARTH FORMATION, COMPRISING: (A) DRILLING A PLURALITY OF SPACED HOLES IN SAID FORMATION; (B) SAID HOLES BEING SPACED A PREDETERMINED DISTANCE FROM ONE ANOTHER; (C) DEPOSITING A SEALING MATERIAL AND AN EXPLOSIVE MATERIAL IN EACH OF SAID HOLES; AND (D) DETONATING SAID EXPLOSIVE MATERIAL; (E) SAID PREDETERMINED DISTANCE BETWEEN SAID HOLES BEING SUCH THAT THE PRESSURE CREATED BY DETONATION OF SAID EXPLOSIVE MATERIAL IS SUFFFICIENT TO FORM INTERCONNECTING FRACTURES BETWEEN SAID HOLES AND DISTRIBUTE SAID SEALING MATERIAL THROUGHOUT SAID FRACTURES BETWEEN SAID HOLES, WHEREBY A PRACTICALLY CONTINUOUS LAYER IS FORMED ACROSS THE EARTH FORMATION BY SAID SEALING MATERIAL. 